1. Field of the Invention
The present invention relates to a new process for manufacturing inner tubes of the so-called puncture-proof type for wheels ensuring carrying or guiding functions for mobile masses and to puncture-proof inner tubes obtained by this process.
2. Description of the Prior Art
Pneumatic tires of the so-called "puncture-proof" type in accordance with the prior art are known. Such pneumatic tires include a toric cushion made from an elastomer material. The toric cushion includes recesses or cells preferably of tubular or cylindrical section, positioned transversely to the tread. Cells are independent of each other, and inflated to a predetermined pressure at the time of manufacture with an appropriate gas. This pressure is fixed at a constant value.
Pneumatic tires of the so-called "puncture-proof" type are also known, which includes a toric cushion as described above but housed into the cover at the base and against the side-walls of said cover so that the upper part of the inner space of the cover is free and inflated to a pressure depending on the requirements of use of the pneumatic tire by means of an external valve connected to the inner space through a supply conduit which passes through the toric cushion. In such pneumatic tires, the pressure can be varied at will.
However, because of their alveolar structure, the so-called puncture-proof inner tubes formed by a toric cushion provided with cells independent of each other, proposed in accordance with the prior art, present difficulties of manufacture: a conventional process for manufacturing these inner tubes consists in forming halves of inner-tube sections, substantially semi-toric in shape, by extrusion for example, then in joining together two symmetrical half-sections thus obtained, by their respective flat faces, by assembling with a solvent, after which the multiple sections thus obtained, necessary for forming the toric cushion are joined together generally also by means of a solvent. The manufacture of a toric cushion with cells, in accordance with the prior art, requires then a multiplicity of operations not only in the manufacture properly speaking but also in the operations for assembly by means of an adhesive, which makes this manufacture long, wasteful of labor and expensive. Moreover, the multiplicity of assembly joints presents a risk of leakage of the pressurized gas contained in the cells and, consequently, a risk of impairing the characteristics proper to this type of inner tube whose value resides precisely in the fact that the presence of a gas under a constant pressure in the cells should make these inner tubes insensitive to perforations.
Attempts have been made to get over these difficulties by proposing so-called puncture-proof inner tubes formed by juxtaposition of two annular elements in the form of semi-tores, by their symmetrical flat faces, these annular elements comprising recessed holes forming cylindrical cells obtained by molding at the same time as the semi-toric annular elements themselves.
It has however proved that the molding process recommended in accordance with the prior art does not in practice allow cells to be obtained, these latter closing up again as soon as the corresponding projections of the mold had been withdrawn from the molded mass.
Consequently, the only technique existing at present for forming, in the half-sections, cylindrical recessed holes which form cylindrical cells when two symmetrical semi-sections are assembled by their flat faces, consists in piercing cylindrical holes in the mass of elastomer. Such a technique requires manual operation and is therefore wasteful of labor: furthermore, manual formation of the recessed holes limits the geometry thereof to the cylindrical form; moreover, it is prejudicial to the regularity of the shape and of the distribution of the cells, and it does not allow a strictly constant repetition of the product, thus causing variations in weight, dimensions and mechanical characteristics of the inner tubes contained.